In order to realize miniaturization of devices such as semiconductor devices, it is necessary to form patterns having dimensions smaller than the critical dimensions obtained by microfabrication using an existing photolithography technique. An extreme ultraviolet (EUV) technology which is a next-generation exposure technique or the like has been developed as a method for forming the patterns with such dimensions. In the EUV technique, light having a significantly shorter wavelength than the UV light source wavelength in the related art is used, for example, light having a very short wavelength of 13.5 [nm] is used. In addition, as a technique substituting the existing lithography technique, a directed self-assembly (DSA) technique for forming a pattern by using a self-assembled block copolymer (BCP) which is one of self-assembled materials that spontaneously organizes an order pattern has attracted attention.
In a case where narrow pattern etching is performed using the above EUV technique and DSA technique, the mask becomes fragile due to the narrow pattern, and collapse of the mask may occur. In contrast, a technique for protecting a mask is disclosed in Patent Literatures 1 and 2.
A plasma etching performance enhancing method disclosed in Patent Literature 1 is to form a characteristic portion by etching without bowing in a dielectric layer on a semiconductor wafer, by etching a structure defined by an etch mask using plasma. In the technique of Patent Literature 1, a mask is formed on a dielectric layer, protective silicon-containing coating is formed on the exposed surface of the mask, and the characteristic portion is formed through the mask and the protective silicon-containing coating. Further, in another method, the characteristic portion is partially etched prior to forming the protective silicon-containing coating. Thus, in the technique of Patent Literature 1, a method is proposed in which the protective silicon-containing coating is formed on the resist mask or on the side wall of the partially etched characteristic portion by using plasma, the mask is protected by the protective silicon-containing coating formed in this way, the critical dimensions (CD) is shrink controlled, and bowing is controlled by etching.
An object of a plasma etching method disclosed in Patent Literature 2 is to prevent and suppress line wiggling and striation caused by the collapse of a pattern or the like after plasma etching of a silicon oxide film or the like using a multilayer resist mask. In the technique of Patent Literature 2, in the plasma etching method for plasma-etching a film to be etched by using a multilayer resist mask, the multilayer resist mask includes an upper layer resist and a lower layer resist, and the method includes a side wall protective film forming step of forming a side wall protective film on the side wall of the lower layer resist. Thus, in the technique of Patent Literature 2, in order to prevent line wiggling and striation, it has been proposed to form a side wall protective film on the mask of a three-layer structure after processing of the lower layer resist and to prevent line wiggling and striation during etching after the formation.